Storage tank for liquids and method of making same

ABSTRACT

A tubular, metallic storage tank for liquid and the method of making same, including a side wall and a bottom, said side wall comprising a plurality of welded together metal plates having a predetermined thickness, and a reinforcing layer of welded together metal plates welded to and covering a lower portion of the side wall and having a predetermined thickness so as to impart sufficient strength to the tank to withstand forces due to liquid stored in the tank, while at the same time the thickness of the said plates is such as to eliminate the need for stress relieving of weld seams between adjacent plates.

United States Patent 1191 3 ,861,552 Adams Jan. 21, 1975 STORAGE TANK FOR LIQUIDS AND A METHOD OF MAKING SAME Inventor: John 11. Adams, Pittsburgh, Pa.

Pittsburgh-Des Moines Steel Company, Pittsburgh, Pa.

Filed: Oct. 20, 1972 Appl. No.: 299,229

Assignee:

References Cited UNITED STATES PATENTS FOREIGN PATENTS OR APPLICATIONS 1,145,344 5/1963 Germany .(220/71 612,252 11/1960 ltaly 220/1B Primary Examiner-William 1. Price Assistant Examiner.loseph Man- Fu May Attorney, Agent, or FirmSh0emaker and Mattare [57] ABSTRACT A tubular, metallic storage tank for liquid and the method of making same, including a side wall and a forces due to liquid stored inthe tank, while at the same time the thickness of the said plates is such as to eliminate the need for stress relieving of weld seams between adjacent plates.

8. Claims, 10 Drawing Figures PATENIEB JANE 1 I975 SHEET 2 UF 2 FIG] STORAGE TANK FOR LIQUIDS AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION This invention relates to large storage tanks for storing liquids such as petroleum products and the like. More particularly, this invention relates to large, flat bottom storage tanks wherein the side wall thereof comprises a plurality of layers of plates welded together to thus impart sufficient strength to the side wall to withstand applied loads thereon from the liquid stored in the tank and at the same time to permit the use of plate thicknesses not greater than the maximum allowable thickness at which stress relieving of weld seams is not required.

' In the United States, storage tanks to be used'in the petroleum industry for storage of petroleum products are manufactured according to a standard written and governed by the American Petroleum Institute called API Standard 650 Welded Steel Tanks for Oil Storage. This standard isgenerally applicable only within the United States, and in other countries this standard or other standards and/or codes may be used. These standards and/or codes are intended to place restrictions on the materials'and the procedures or methods used in constructing tanks to insure a workable safe design. Onerestriction of the API standard is that the and the required plate thickness exceeds l k inches, it

becomes necessary to stress relieve the weld joints bea tween adjacent plates, and this process is time consuming and very expensive. Accordingly, the construction of large tanks wherein the plate thickness are such as v to require stress relieving is prohibitively expensive.

There is a. demand in industry for tanks of ever increasing size and as the size increases, the thickness of the plates used in the side walls of the tanks also increases. Consequently, in the 'prior art, tank designs are called for wherein the resulting required wall thickness is greater than the maximum thickness allowed without stress relieving. Various attempts have been made in the prior art in storage tanks and other vessels to construct tanks or vessels from a plurality of plates welded together at adjacent peripheral edges thereof with the thickness of the plates being less than the maximum thickness allowed without stress relieving. For example, in one prior art construction doubly curved plates are used in order to obtain the proper strength of the side wall without having to use plates with a thickness exceeding the thickness at which stress relieving is required. This method, however, is quite expensive and storage tanks, as contemplated by the present invention, would be economically prohibitive if constructed with doubly curved plates in the side wall thereof. Other methods have also been used,'such as the provi sion of one or more narrow reinforcing rings or bands around the outside lower portion of the sidewall of large storagetanks. However, this construction is only With the present invention a unique and novel construction is used in the side wall of the storage tank which enables extremely large storage tanks to be built usingplates with a thickness which does not require stress relievingpln particular, in accordance with the invention, a plurality of layers of plates are welded together, including at least an inner layer and an outer layer, with the plates in the outer layer staggered or offset relative to the plates in the inner layer so that the weld seams between adjacent plates in the inner and outer layers are staggered or offset relative to one another. Thus, the combined thickness of the layers en- I requiring stress relieving of the weld seams between adjacent plates in the layers. Thus," tanks of unlimited size can be economically constructed.

A further advantage of such construction is in the process of welding the plates together. Frequently, a butt weld is used between adjacent edges of adjacent plates in order to weld the plates together. Quite often when thick plates arebutt welded, there is an initial gap between the two plates before the welding starts. This gap is provided because of the shrinkage that occurs in the weld during the welding process. In the prior art, when both sidesof the weld are not accessable, a backup plate is positioned on the far side of the weld and all of the welding operation is performed from the near side of the weld. The backup plate serves as a bridgeupon whichthe initial layers of weld metal are deposited in order to weld across the gap and provide full weld penetrationfln fact, the use of these backup plates is necessary in such welding. However, the backup plates constitute, another step in the welding process since after the weld has been deposited and the weld completed, the backup plate is often removed to improve performance and appearance of the .weld. This additional step in the welding process increases the total weld cost in the construction of such tanks..

With the present invention,.the adjacent inner and outer layers each serves as a backup or bridge for the other layer in the tank construction. Thus, while welding the seam between the plates in one layer, the other layer serves as a backup or bridge for the weld metal deposited in the gap between adjacent plates, thus reducing the total weld costs and eliminating a need a backup plate at the weld joints.

OBJECT OF THE INVENTION for It is an object of this invention to provide a large storage tankand method of constructing same, wherein the side wall of thetankcomprises a plurality of layers of plates welded together to thus impart sufficient strength to the side wall of the tank to withstand loads and stresses thereon, while at the same time enabling plate thicknesses to be used which do not require stress relieving at the weld seams.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top perspective view ofa tank constructed I FIG. 3 is a fragmentary view in elevation taken along line 3-3 in FIG. 2 and showing the staggered relationship and overlap between the plates in the inner and outer layers.

FIGS. 4 through are illustrations of various steps in the process of constructing a tank in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION In the drawings, wherein like reference numerals indicate like parts throughout the several views, a storage tank is indicated generally at T in FIG. 1 and comprises a cylindrical side wall W having a roof R on top thereof, a flat bottom B and an annular footer plate F surrounding the bottom B and on which the side wall is supported. The side wall W comprises a plurality of plates P1 welded together at their peripheral edges to form an inner layer L1, and a plurality of plates P2 are welded together at their peripheral edges and to the plates P1 in the inner layer L1 to form an outer, reinforcing layer L2. The outer layer L2, as seen in FIGS. 1 and 2-, extends only over a portion of the side wall W near the lower end of the side wall where the greatest wall thickness or plate thickness is required in order to withstand the loads and stresses thereon due to the head or pressure of liquid stored in the tank.

The relationship of plates P1 and P2 and of layers L1 and L2 to one another and to the side wall W are clearly seen in FIGS. 2 and 3. The plates P1 in the inner layer L1 are welded together along their peripheral edges at vertical and horizontal weld seams Sv and Sh, respectively, to form a first annular ring R1, in which the plates have a first predetermined thickness t supported on the footer plate F substantially medially of the inner and outer peripheral edges of the footer plate. A second ring R2 is superposed or stacked on the ring R1, and the plates in ring R2 also have a predetermined thickness t. A third ring R3 is superposed or stacked on top of ring R2 and the plates in ring R3 have a predetermined thickness tl, greater than thickness t. A fourth ring R4 is superposed or stacked on top of ring R3, and the plates in ring R4 have a predetermined thickness r2, greater than thickness I but less than thickness tl..

The plates P2 are similarly welded together along vertical and horizontal weld seams Sv and Sh, respectively, to form a bottom ring R1 welded to the outer surface of the plates in layer L1, with the bottom edge of ring R1 spaced above the footer plate F a distance or elevation hl. The upper edge of ring R1 extends above the upper edge of ring R1 a distance y so that the horizontal weld seams Sh of the outer layer L2 are vertically staggered or offset with relation to the horizontal weld seams Sh of the inner layer L1. Similarly, the vertical weld seams Sv' of the outer layer L2 are staggered or offset horizontally from the vertical weld seams Sv of the inner layer L1 by a distance x.

The outer layer L2 also includes a second ring R2 in vertical juxtaposition to ring R1 and welded to the ring R1 and to the plates comprising the inner layer L1. The upper edge of the outer layer L2 is spaced above the footer plate F a distance h2.

The dimensions hl and h2 and the number of layers in the side wall W of the tank are based upon the size of the tank. Thus, although only two layers L1 and L2 are illustrated in the particular embodiment described, as many layers as necessary may be used in fabricating the side wall W, and the extent to which layer L2 covers layer L1 may be changed as desired or necessary, depending upon the size and height of the tank, since the hoop load in the shell at the bottom of the tank increases as the size of the tank and the depth of stored liquid increases.

In one specific example, a tank constructed in accordance with the invention has a two million barrel capacity, a diameter of 505 feet 4 inches and a height of 56 feet. The plates in rings R1, R2, R1 and R2 all have a thickness 1 of about 1.05 inches and the bottom edge of ring R1 is spaced upwardly from the footer plate F a distance hl of 24 inches. The upper edge of ring R2 is spaced upwardly from the footer plate a distance h2 of 198 inches, or, in other words, the layer L2 covers and reinforces the inner layer L1 over a vertical distance of about I74 inches. The plates in ring R3 have a thickness t1 of 1.44 inches and the plates in ring R4 have a thickness :2 of 1.30 inches, and the horizontal and vertical weld seams Sh, Sv, Sh in the inner and outer layers L1 and L2, respectively, are spaced or offset from one another distances x and y of about 6 inches.

It is not necessary that the bottom edge of layer L2 extend all the way to the footer plate F since the connection of the bottom of the sidewall with the bottom B of the tank serves to reinforce the bottom portion of side wall W by virtue of its ability to restrain the radial growth of the bottom portion of the side wall.

The method or steps of constructing the tank are illustrated in FIGS. 4 through 10. In FIG. 4, the plates Pl comprising the bottom ring R1 are positioned on the footer plate F and tack welded in place. In FIG. 5, the plates P2 comprising ring R1 in the outer layer L2 are positioned on the outer surface of ring R1 and the plates of ring R1 are tack welded along the vertical and horizontal seams Sh and Sv' thereof. In FIG. 6, the plates of ring R2 are positioned on top of ring R1 and welded along the vertical and horizontal seams Sv and Sh thereof. The welding of the vertical and horizontal seams of rings R1 and R1 is also completed at this time. In FIG. 7, the plates of ring R2 are positioned around the outside of ring R2 and on top of ring R1. and tack welded along the vertical and horizontal seams thereof, and the welding of the vertical and horizontal seams of ring R2 is completed at this time. In FIG. 8, the plates of ring R3 are stacked or placed on top of ring R2. and the vertical and horizontal seams thereof are tack welded, and the welding of the horizontal and vertical seams of ring R2 is completed. In FIG. 9, the plates'of ring R4 are positioned on top of ring R3 and welded, and subsequent rings are placed on top of one another and welded in a conventional manner until the side wall of the tank is completed. By this method of construction, the plates of the outer rings or layer serve as a bridge or backup for the weld metal as the seams between the plates of the inner layer are welded from the inside of the tank, and the plates of the inner layer serve as a bridge or backup for the weld metal as the seams of the outer layer are welded from outside the tank. See FIGS. 6, '7 and 10, and note the relationship between the layers L1 and L2 and a welding implement WI.

The tank need not have a fixed roof R as shown, but could have a floating roof (not shown), or it could have both a floating roof or cover and a fixed roof, or no roof or cover at all. Further, the tank could have any size and configuration within the scope of the invention and the plates in the various rings could have any necessary thickness, less than the thickness at which stress relieving is required.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents, are therefore intended to be embraced by those claims.

What is claimed is:

l. A tubular metallic storage tank for liquid including a cylindrical side wall and abottom wall, said side wall comprising a plurality of metal plates each of substantially the same radius of curvature as the radius of curvature of the tank side wall and said plates welded together in edge-to-edge relationship, tank reinforcing layer means extending about the tank comprising metal plates welded together at adjacent edges and welded to, covering, and in contact with a substantial lower outer portion of the adjacent side wall of the tank, said reinforcing layer plates having a vertical width substantially the same as the vertical width of the plates in the tank side wall, the thickness of each of the plates being such that the need for stress relieving of the weld seams between adjacent plates is eliminated, all of said plates having a predetermined combined thickness to impart sufficient strength to the tank to withstand forces due to liquid stored in the tank, and the weld seams between adjacent plates in the reinforcing layer being offset from the weld seams between adjacent plates in the tank side wall.

2. A storage tank as in claim 1, wherein the side wall comprises a plurality of annular rings of welded together plates, said rings welded together in vertically stacked edge-to-edge relationship on top of one another.

3. A storage tank as in claim 2, wherein said reinforcing layer comprises a plurality of annular rings of welded together plates, saidrings welded together in edge-to-edge vertically stacked relationship and welded to the outer surface of the side wall.

4. A storage tank as in claim 3, wherein the rings in said reinforcing layer are vertically offset or staggered relative to the rings in the side wall so that the rings in the reinforcing layer are overlapped with the edges of the rings in the side wall.

5. A storage tank as in claim 4, wherein there are at least four rings in the side wall and at least two rings in the reinforcing layer. I

6. A storage tank as in claim 5, wherein the bottom edge of the reinforcing layer is spaced upwardly from the bottom of the side wall. I

7. A storage tank as in claim 6, wherein the thickness of the plates in the two bottom most rings of the side wall are equal to each other and to the thickness of the plates in the reinforcing layer.

8. A storage tank as in claim 7, wherein the thickness of the plates in the third ring from the bottom of the side wall is greater than the thickness of said 

1. A tubular metallic storage tank for liquid including a cylindrical side wall and a bottom wall, said side wall comprising a plurality of metal plates each of substantially the same radius of curvature as the radius of curvature of the tank side wall and said plates welded together in edge-to-edge relationship, tank reinforcing layer means extending about the tank comprising metal plates welded together at adjacent edges and welded to, covering, and in contact with a substantial lower outer portion of the adjacent side wall of the tank, said reinforcing layer plates having a vertical width substantially the same as the vertical width of the plates in the tank side wall, the thickness of each of the plates being such that the need for stress relieving of the weld seams between adjacent plates is eliminated, all of said plates having a predetermined combined thickness to impart sufficient strength to the tank to withstand forces due to liquid stored in the tank, and the weld seams between adjacent plates in the reinforcing layer being offset from the weld seams between adjacent plates in the tank side wall.
 2. A storage tank as in claim 1, wherein the side wall comprises a plurality of annular rings of welded together plates, said rings welded together in vertically stacked edge-to-edge relationship on top of one another.
 3. A storage tank as in claim 2, wherein said reinforcing layer comprises a plurality of annular rings of welded together plates, said rings welded together in edge-to-edge vertically stacked relationship and welded to the outer surface of the side wall.
 4. A storage tank as in claim 3, wherein the rings in said reinforcing layer are vertically offset or staggered relative to the rings in the side wall so that the rings in the reinforcing layer are overlapped with the edges of the rings in the side wall.
 5. A storage tank as in claim 4, wherein there are at least four rings in the side wall and at least two rings in the reinforcing layer.
 6. A storage tank as in claim 5, wherein the bottom edge of the reinforcing layer is spaced upwardly from the bottom of the side wall.
 7. A storage tank as in claim 6, wherein the thickness of the plates in the two bottom most rings of the side wall are equal to each other and to the thickness of the plates in the reinforcing layer.
 8. A storage tank as in claim 7, wherein the thickness of the plates in the third ring from the bottom of the side wall is greater than the thickness of said two bottom most rings. 